Make `rustc_onunimplemented` export path agnostic

This makes it so that all the matchers that match against paths use the
definition path instead of the export path. This removes all duplication
around `std`/`alloc`/`core`.

This is not necessarily optimal because we now depend on internal
implementation details like `core::ops::control_flow::ControlFlow`,
which is not very nice and probably not acceptable for a stable
`on_unimplemented`.

An alternative would be to just string-replace normalize away
`alloc`/`core` to `std` as a special case, keeping the export paths but
making it so that we're still fully standard library flavor agnostic.

1 files changed, 7 insertions, 4 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
index cbfb06eac7b..9c9b78f4152 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
@@ -180,8 +180,9 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             flags.push((sym::cause, Some("MainFunctionType".to_string())));
         }
 
-        // Add all types without trimmed paths.
-        ty::print::with_no_trimmed_paths!({
+        // Add all types without trimmed paths or visible paths, ensuring they end up with
+        // their "canonical" def path.
+        ty::print::with_no_trimmed_paths!(ty::print::with_no_visible_paths!({
             let generics = self.tcx.generics_of(def_id);
             let self_ty = trait_ref.self_ty();
             // This is also included through the generics list as `Self`,
@@ -296,7 +297,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             {
                 flags.push((sym::_Self, Some("&[{integral}]".to_owned())));
             }
-        });
+        }));
 
         if let Ok(Some(command)) = OnUnimplementedDirective::of_item(self.tcx, def_id) {
             command.evaluate(self.tcx, trait_ref, &flags)
@@ -578,7 +579,9 @@ impl<'tcx> OnUnimplementedDirective {
                     Some(tcx.features()),
                     &mut |cfg| {
                         let value = cfg.value.map(|v| {
-                            OnUnimplementedFormatString(v).format(tcx, trait_ref, &options_map)
+                            // `with_no_visible_paths` is also used when generating the options,
+                            // so we need to match it here.
+                            ty::print::with_no_visible_paths!(OnUnimplementedFormatString(v).format(tcx, trait_ref, &options_map))
                         });
 
                         options.contains(&(cfg.name, value))